The present invention relates to an electric motor, particularly for an actuating device for displacing a control device, such as a valve, a gate valve, a blow-out preventer, or the like, for use in oil and gas production, the electric motor comprising a stator and a rotor assigned to a motor shaft, as well as a position holding device for exerting a holding torque on the motor shaft. The present invention also relates directly to such a position holding device for an electric motor.
The electric motor is connected via the motor shaft, for example, to a screw nut of a thread drive so as to linearly displace a threaded spindle and to axially displace the control device accordingly via said spindle between an advanced position and a retracted position. The position holding device serves to hold a specific position of the motor shaft and thus of the threaded spindle and the control device, respectively, so that particularly the threaded spindle is prevented from returning automatically from a specific position.
Such an electric motor is e.g. described in WO 2008/125136. In this publication the position holding device is directly connected to the motor shaft of the electric motor. Owing to this direct connection, loop or volute springs need for instance no longer be arranged, which springs, on the one hand, allow for a rotation of the motor shaft and the threaded spindle, respectively, in one direction while on the other hand a return torque exerted e.g. by the control device is taken up by said spring.
The corresponding position holding device according to WO 2008/125136 is of an inexpensive and relatively simple construction, while a corresponding fault-proofness of the actuating device and the control device, respectively, is maintained at the same time.
The corresponding position holding device according to WO 2008/125136 is of an inexpensive and relatively simple construction, while a corresponding fault-proofness of the actuating device and the control device, respectively, is maintained at the same time.